Switching voltage regulators are commonly utilized in electronic systems to generate from a received input voltage and current a required output voltage and current for operating components in the electronic system. In operation, a switching voltage regulator turns power transistors, which are typically MOSFETs, ON and OFF rapidly in order to generate the desired output voltage and current. An internal control circuit provides pulse width modulated (PWM) signals to the power transistors to control the ON and OFF state of the transistors. The duration for which a PWM signal is ON divided by the period of the PWM signal defines a duty cycle D of the PWM signal. The internal controller adjusts the duty cycle D of the applied PWM signals to thereby control and regulate output voltage and current. Numerous different types of circuit topologies are utilized for such switching voltage regulators, with the specific type of topology being determined by the application of the switching voltage regulator. For example, the switching voltage regulator may be a step-down converter in which case a Buck converter may be utilized while in other applications a step-up converter such as a Buck-boost converter may be utilized. The Buck converter will be utilized in the following description merely by way of example. The terms “converter” and “voltage regulator” are used interchangeably herein.
Many applications utilize multiphase Buck converters in which a number of individual Buck converters are connected in parallel to a load that is to receive the generated output voltage and current. In such a multiphase Buck converter, each individual Buck converter will be referred to as a stage or phase. The internal control circuit of a multiphase Buck converter generates phase shifted PWM signals to activate the parallel-connected Buck converter stages so that each stage supplies a portion of the overall output power defined by the output voltage and current. Furthermore, the internal control circuit may turn stages ON and OFF depending upon the voltage and current demands of the load connected to the multiphase converter. For example, if the load draws more current from the multiphase converter the internal control circuit may activate more stages while the control circuit may deactivate stages when the load draws less current.
The efficiency of multiphase voltage regulators varies as a function of the number of stages or phases that are activated and as a function of the required load or output current IOUT. The efficiency η of a multiphase converter is defined as input power PIN supplied to the converter divided into the output power POUT supplied by the converter (η=(POUT/PIN). The input power PIN is given by input current IIN times input voltage VIN while output power POUT is given by output current times IOUT times output voltage VOUT. Users of multiphase voltage regulators would like the internal control circuit to detect IIN, VIN, IOUT, and VOUT so that the efficiency q of the regulator can be calculated in real time and operation of the regulator controlled in response to the detected efficiency to thereby improve the overall efficiency of the regulator.
FIG. 1 is a graph illustrating efficiency η as a function of output current IOUT for a four-stage or four-phase voltage regulator. A first line 100 shows the efficiency of the regulator for a single phase, meaning that one of the four stages in the multiphase converter is activated. A line 102 in the graph illustrates the efficiency of the converter for two phases, a line 104 shows the efficiency for three phases, and a line 106 illustrates the efficiency for four phases. As seen from the graph, the efficiency η of the converter varies as a function of the output current IOUT and as a function of the number of phases activated. Moreover, for a given output current IOUT the efficiency η of the regulator can be improved by controlling the number of phases that are activated. For example, if the output current IOUT is 75 amps then activating three phases optimizes the efficiency η while two phases optimize efficiency when the output current equals 30 amps. Ideally, the phases of the multiphased voltage regulator would be controlled so that the efficiency η of the regulator is as shown through the bold line in FIG. 2. FIG. 2 is a graph illustrating efficiency η as a function of output current IOUT and includes a bold line 200 corresponding to the portions of the respective lines 100-106 in FIG. 1 that would ideally be tracked by the converter during operation in order to optimize the overall efficiency of the converter.
In conventional approaches for optimizing efficiency of a multiphased voltage regulator, current thresholds are utilized to determine whether to activate or deactivate phases during operation. For example, referring back to FIG. 1 a first current threshold may be set at approximately 22 amps such that when the output current IOUT exceeds this threshold an additional phase is activated. In this case, the regulator operates with a single phase for output currents IOUT up to 22 amps and then once the output current exceeds 22 amps the internal control circuit activates a second phase so that the regulator now operates with two phases. In the example of FIG. 1, a second current threshold may be set at approximately 37 amps so that once the output current IOUT exceeds 37 amps the internal control circuit activates another phase so that the regulator now operates with three phases. A final current threshold may be set at approximately 53 amps so that when the output current IOUT exceeds this threshold the internal control circuit activates the fourth and final phase of the regulator so that the regulator now operates with four phases.
With this conventional approach, current thresholds cannot always be set so that the efficiency η of the regulator is optimized over the entire range of output currents IOUT. For example, referring back to FIG. 1 a circle 108 is drawn around lines 102 and 104 at an output current IOUT of approximately 30 amps. Note that if a current threshold was set at 30 amps so that the regulator would switch at this point from two-phase operation to three-phase operation the efficiency of the regulator would not be optimal as shown in the graph by the efficiency for two-phase operation corresponding to line 102 being greater than the efficiency for three-phase operation corresponding to the line 104.
Improved systems and methods for the control of multiphase regulators to improve the efficiency of operation of such regulators are desirable.